Efraim Halevy, head of the Mossad from 1998 to 2002 believes that WMDs may yet be found in Iraq. In an online Q&A session, he replied to a question about the missing WMDs:

You might be surprised if I say that not withstanding the fact that weapons of mass destruction have not yet been found in Iraq, I would not rule out the possibility that they might be found in the future. Iraq is a vast country, and only several months ago, a full squadron of aircraft was discovered buried in the sand.

I do not believe that Saddam Hussein risked the fall of his regime and his own capture just out of false pride. He doggedly and continuously refused to cooperate with the United Nations missions which tried time and time again to set up a credible monitoring system in Iraq after 1998.

I know this reply goes against some of the very definitive statements that have come out of Washington in recent months, following the findings of the Senate select committee on the Iraqi campaign and I know that there have been others who have searched Iraq high and low and who have not come up with anything in their hands. Yet all I can do is commend to you the findings of the British commission set up under the leadership of Lord Butler. Butler concluded in his report that he could not state definitively that weapons of mass destruction would never be found in Iraq.
Haaretz - QA